Process for the production of alkalisoluble cellulosic textile materials by etherifying the cellulose with specific ether groups and oxidizing with nitrogen dioxide



Patented Sept. 4, 1952 fine 3,052,511 PROCESS FOR THE PRODUCTTON F ALKALI- SOLUBLE CELLULOSEC TEXTILE MATERIALS BY ETHERIFYING THE CELLULUSE WITH SPECIFIC ETHER GROUPS AND OXiDlZING WITH NITRQGEN DIOXIDE Robert M. Reinhardt and John David Reid, New Orleans,

La., assignors to the United States of America as represented by the Secretary of Agriculture No Drawing. Filed Feb. 23, 1960, Ser. No. 10,522 8 Claims. (Cl. 8-420) (Granted under Title 35, U.S. Code (1952), sec. 266) A non-exclusive, irrevocable, royalty-free license in the invention herein described, throughout the world for all purposes of the United States Government, with the power to grant sublicenses for such purposes, is hereby granted to the Government of the United States of America.

In Patent No. 2,938,765 there is disclosed a process for the production of alkali-soluble cotton textile materials by an exceedingly mild chemical modification of the original textile material followed by an oxidizing treatment that employs, in combination, two oxidizing reagents in dilute aqueous solution. In the process of this patent, oxidation of the mildly chemically modified cotton with one oxidizing reagent in combination with a second oxidizing reagent was found to be unexpectedly and strikingly synergistic.

It is well known that certain chemical modifications of cotton such as, for example, carboxymethylation and aminoethylation are effective for the production of water or alkali-soluble cotton textile material. It is also known that if the chemical modification treatments referred to above are followed by a subsequent oxidizing processing step using organic or inorganic oxidizing reagents, that the ultimate alkali-solubility of the treated material is enhanced to a considerable degree.

Conventional processes for the production of alkalisoluble cotton textile materials with solubilities in excess of 95% involve a chemical modification pretreatment of the textile material to produce a product with a degree of substitution (average number of substituent groups per anhydroglucose unit of the cellulose chain) of at least 0.4, followed by a rigorous oxidation treatment using either concentrated oxidizing reagents or, if dilute oxidizing reagents are employed, unduly long oxidizing times and high oxidizing temperatures. The combination of chemical modification to produce a product with a high degree of substitution followed by a vigorous oxidizing step gives rise, in the conventional processes, to serious loss of all desirable textile properties.

The object of the present invention is to produce an alkali-soluble cellulosic textile material by employing (a) a chemical modification treatment carried to a low degree of substitution, in the range of from about 0.01 to about 0.33, preferably in the range of about 0.0 2 to 0.12, and hence of small import insofar as the original characteristics of the untreated fibrous cellulosic material is concerned and (b) a highly effective oxidation step carried out on the chemically modified fibrous cellulosic material by the use of nitrogen dioxide, either in the gaseous or liquid phase, in solution in an inert organic solvent, or generated in situ from aqueous solutions of nitrite salts and aqueous acids.

The term nitrogen dioxide is used herein to designate the equilibrium mixture of nitrogen dioxide (N0 and nitrogen tetroxide (N 0 which normally exists under the various conditions of use.

An unexpected, and strikingly synergistic effect results from the combined chemical modification-oxidation procedure of the present invention which permits the use of milder conditions and shorter times of oxidation, and results in greater retention of the original fiber properties While achieving high solubility of the processed material in dilute solutions of alkaline materials.

The true synergism of the process is illustrated by analysis and solubility determinations of two samples: (a) cotton partially carboxymethylated to 3.1% COOI-I content, then oxidized with nitrogen dioxide to 5.7% total carbonyl content or 2.6% oxidation carboxyl content; and (b) rnercerized cotton, oxidized with nitrogen dioxide to 5.7 oxidation carboxyl content. The carboxymethylated-oxidized sample was 93% soluble in 1% sodium hydroxide solution while the mercerized-oxidized sample was only 35% soluble in 1% sodium hydroxide solution. Comparison at equal total carboxyl content shows the synergistic effect of the combined etherificationoxidation treatment to produce more than 2.5 times as much solubility as the oxidation step alone on mercerized fabric. However, if considered on the basis of oxidation carboxyl alone, the effect is even more striking. Less than half the degree of oxidation has produced more than 2.5 times as much solubility.

By the process of the present invention, useful cellulosic textile materials are prepared which are soluble in more dilute and more mildly alkaline solutions than are the products of the aforesaid Patent No. 2,938,765. The cellulosic textile products of the present invention exhibit solubility in 1% aqueous sodium hydroxide, in 1% aqueous sodium carbonate, in 1% aqueous ammonium hydroxide, and in other dilute aqueous mildly alkaline solutions.

Cellulosic textile products of prior art oxidation processes require stronger and more concentrated alkali to disintegrate and dissolve the fibrous products. For example, textile material produced by the chromic acid oxidation of partially etherified cotton requires the use of about 10% aqueous sodium hydroxide to achieve solution of the textile material.

The preservation of the original textile properties in an alkali-soluble textile material is most valuable and highly desirable since, even though for many uses the presence of the alkali-soluble material is transient, it is essential that the alkali-soluble product, while it exists in textile form, be capable of being processed on conventional textile machines. The obvious requisites are, of course, retention of strength, flexibility and abrasion resistance. A typical use for an alkali-soluble textile material is as a scaffolding or supporting foundation for the preparation of light or novelty yarns and fabrics. By alternating soluble textile yarn with nonsoluble textile yarns in weaving and then subjecting the woven product to dissolution, open-work fabrics and other novelty effects may be achieved. Knit socks may be produced in a continuous string each connected to its neighbors by a thread of soluble yarn. The socks after fabrication may then be readily separated by simple disintegration of the soluble connecting yarn. Soluble textile materials are also used as backing in the manufacture of lace. In the medical field, soluble textile materials have found applications as bandages, compresses and sutures. Other uses will be apparent to those skilled in the art.

In general the process of this invention is carried out by chemically modifying a fibrous cellulosic material to produce alkali-soluble products. Methylation, ethylation, carboxymethylation, carboxyethylattion, phosphonomethylation, aminoethylation, hydroxyethylation, carbamoylethylation, sulfoethylation, and the like may be employed as the chemical modification step. The preferred chemical modification for the process of this invention is partial etherification applied as described in the specific examples that follow. Regardless of the chemical modification treatment employed, the advantageous feature of the process of this invention is that the chemical modi of alkali-soluble derivatives by oxidation.

fication need not be carried beyond a degree of substitution of about 0.33. The preferred range for this process is a degree of substitution of about from 0.02 to 0.12 of methyl, ethyl, carboxymethyl, carboxyethyl, phosphonomethyl, aminoethyl, etc. groups introduced by virtue of the above chemical modification procedures. Aside from the consideration of retaining the textile properties of the chemically modified material, the possibility of operating at a low degree of substitution possesses o-bivous economic advantages. Following the chemical modification step, which step is to produce a material with a low degree of substitution and a material virtually unchanged with respect to textile properties, the chemically modified fibrous cellulosic material is subjected to an oxidation with nitrogen dioxide. The oxidation step can be carried out at a temperature within the range of from about C., to about 100 0, higher temperatures requiring shorter reaction times. It is generally preferred to carry out the oxidation at room temperature (20 to 40 C.), since it is 'convenientand economical to operate at this temperature .to 25 hours.

The nitrogen dioxide can be employed in the gaseous phase, preferably at normal atmospheric pressure; or at a pressure above normal atmospheric pressure; in the .liquid phase; in solution in an inert organic solvent, such as benzene or carbon tetrachloride, said solution having a concentration in the range of about from 1 to 25% nitrogen dioxide by weight; or it can be generated in situ by treatment of the chemically modified fibrous cellulosic material with aqueous solutions of nitrite salts, such as potassium nitrite or sodium nitrite, and with aqueous acid solutions, such as a solution of ortho-phosphoric acid.

There are three main points of attack by oxidizing agents on the cellulose molecule: (1) The aldehyde group on carbon atom 1 of the terminal anhydroglucose unit of the cellulose chain; however, in cotton with its relatively high degree of polymerization the number of these present is small and of little importance in this study. (2) The hydroxyl group on carbon atom 6 with formation of aldehyde or carboxyl group, depending upon reagent used. (3) The 2,3-dihydroxy or glycol group which may be oxidized either simultaneously or individually without ring cleavage to form ketonic groups or with ring cleavage to form aldehyde groups. The latter may be further oxidized and converted to carboxyl groups.

Certain reagents in their reaction with cellulose are specific and result in almost exclusive oxidation at the 2,3 or at the 6 positions of the glucose residues. Nitrogen dioxide has been shown to react preferentially but not exclusively at the 6 position, oxidizing the primary alcohol group to a carboxyl group. However, other side reactions have been noted which result in oxidation at other points in the cellulose chain. Among the side reactions reported are those which introduce aldehyde and keto groups. The oxyceluloses bearing carboxyl groups at the 6 position and those which bear aldehyde or keto groups at the 2,3 positions are soluble in alkali.

Partially etherified cottons offer two principal theoretical advantages over untreated cotton for the production These advantages are: (1) Presence of solubilizing groups which enhance alkali-solubility through greater solubility of the alkali-cleaved fragments. 2) Opening up of the crystalline regions of the fiber for more uniform and increased reaction. These properties are achieved by variations in the methods of preparation and chemical nature of the substituent group introduced.

Many etherified cottons bear a substituent group which in itself confers solubility upon the derivative. Oxidation of unsubstituted fi-alcohol groups to carboxyl groups introduces another solubilizing group. Oxidation of unsubstituted 2, 3 glycol units causes alkali-liability. The combined efiects added together result in high solubility from relatively low degree of reaction. A small amount of oxidation causing a limited amount of cleavage in alkali can be very effective if the cleaved fragments hear analkali-solubilizing group. Thus, fragments of longer chain length than are usually soluble, will go into solution. Therefore, the alkali-solubility of oxidized partially etherified cotton theoretically combines disintegration with true macromolecular solution.

Having thus described in a general way the operation of the process of this invention, details of the process are listed below in specific examples which describe the application of the process to cotton textile materials.

The following examples will serve to illustrate the invention but should not be considered to be limiting. Prodnets with many different variations of properties may be obtained by further changes of the variables of the process which are principally the degree of substitution of the chemically modified fibrous cellulosic material, the time and temperature of the oxidation reaction, and the oxidizing system being employed.

In the examples given below, the solubilities of the various cellulosic textile materials in 1% NaOH solution were determined by the following procedure: Approximately 1 gram of cellulosic textile material was accurately weighed on an analytical balance to four decimal places. The sample was transferred to an Erlenmeyer flask and aqueous 1% NaOH solution added in :1 liquor to sample ratio (by weight). The flask was allowed to stand for 30 minutes at room temperature (25 C.) with swirling every 5 minutes. At the end of the 30 minute period, the solution and residue were quantitatively transferred to a previously weighed centrifuge tube. The tube was then centrifuged at 1700 r.p.m. for 8 minutes to effect separation of residue and clear supernatant solution. The solution was decanted and the residue washed twice with distilled Water, twice with dilute acetic acid solution and four times with distilled water. The residue was then dried, equilibrated, and weighed on the analytical balance. From the weight of the residue, the percent solubility of the sample was calculated:

wt. of residue Percent solubllrty- 100 m X 100) Similarly, the solubility of cellulosic samples was determined in other solvent solutions using this technique.

Example 1 Samples of cotton cloth, untreated and pretreated as follows: (a) carboxymethylated by treatment with 17% aqueous chloroacetic acid and 50% sodium hydroxide, degree of substitution of 0.10; (b) carboxyethylated by hydrolysis of cyanoethylated cotton with 20% sodium hydroxide solution, degree of substitution 0.12; (c) phosphonomethylated by treatment with 6.8% disodium salt of chloromethylphosphonic acid in the presence of 25 sodium hydroxide, degree of substitution 0.04; (d) alphamethyl carboxymethylated by treatment with 25% aqueous solution of alpha-chloropropionic acid and 50% sodium hydroxide, degree of substitution 0.02; (e) methylated by treatment with 50% sodium hydroxide and a toluene solution containing 0.5 mole of dimethyl sulfate for each mole of NaOH, degree of substitution 0.62; (f) aminoethylated by treatment with 20% aqueous Z-aminoethyl sulfuric acid and 40% sodium hydroxide, degree of substitution 0.08; and (g) mercerized, were Washed and airdried. The fabrics were then oxidized with an excess of gaseous nitrogen dioxide at atmospheric pressure and room temperature (25 C.) for one hour, for two hours, and for four hours. The nitrogen dioxide from a compressed gas cylinder was admitted to the reaction tube containing the fabric sample and the displaced air swept out. After reaction the fabrics were washed with methyl alcohol, then with distilled water and air-dried. Solubilities of the various fabric samples in 1% aqueous sodium hydroxide and in 1% aqueous sodium carbonate, determined by the aforementioned procedure, are shown in the following table:

Oxidized 1 hr. Oxidized 2 hrs. Oxidized 4 hrs.

Percent Solu- Percent Solu- Percent Solu- Fabric Oxidized bility inbility inbility in- 1% 1% 1% 1% 1% 1% NaOH Na CO NaOH N32003 NaOH Nazco Untreated cotton. 12. 10. 5 37. 5 39.0 41. 5 37. 7 Carboxymethylated cotton 1- 95. 4 94.3 99. 2 98. 5 99. 6 97. 6 Carboxyethylated cotton 99. 0 96. 2 99. 4 97.9 99.7 99. 1 Phosphonomethylated cotton 69. 0 52. 8 99. 4 98. 8 99. 8 99. 5 Alpha-methyl carboxy-methylated cotton 1 56. 7 39. 0 94. 3 78.0 98. 8 96.0 Methylated cotton 94. 7 96. 1 99. 7 98. 8 99. 6 99. 2 Aminoethylated cotton 80. 3 61. 3 99. 2 98. 0 99. 5 97. 6 Mercerized cotton 25.0 21. 1 60. 8 46. 9 73. 1 55. 2

Example 2 Samples of mercerized cotton cloth and of partially carboxymethylated cotton cloth, degree of substitution 0.1, were oxidized with an excess of gaseous nitrogen dioxide at atmospheric pressure and room temperature (25 C.) for periods of time ranging from 4 hour to 25 hours. After reaction, the fabrics were washed with methyl alcohol, then with distilled water and air-dried. Solubilities of the fabrics in 1% aqueous sodium hydroxide, in 1% aqueous sodium carbonate, and in 1% aqueous ammonium hydroxide are shown in the following table:

Oxidized-Untreated Cotton Oxidized-Carboxy'methylated Cotton Time of Oxifiiation Percent Solubility i.u Percent Solubility in- 1% 1% 1% NaOH Na OO NH OH NaOH Na CO In addition to having greater solubility, the strength of the oxidized-carboxymethylated fabric was greater than that of the merccrized fabric after oxidation. For example, after 4 hours of treatment with nitrogen dioxide, the carboxymethylated cotton retained 79% of its original strength, the mercerized 55%. After 25 hours of treatment, retentions were 68% and 48%, respectively.

Example 3 The effect of variation of the degree of substitution of the chemically modified cotton is illustrated in this example. Cotton cloth was carboxymethylated to degrees of substitution of 0.04, 0.06, 0.08, and 0.10. These fabrics were oxidized with an excess of gaseous nitrogen dioxide at atmospheric pressure and room temperature (about 25 C.) for reaction times of minutes, 30 minutes, 1 hour, and 2 hours. For comparison, samples of untreated cotton and of mercerized cotton were similarly treated.

Solubilities of the fabric samples in 1% aqueous sodium hydroxide solution are shown in the following table:

Percent Solubility in 1% NaOH 5 after Oxidation Time of- Fabric Oxidized 15 30 1 2 minutes minutes hour hours Untreated cotton 14.6 17.8 49. 7 62. 6 1O Mercerized cotton 12.7 18.3 38.2 81.0

Oarboxymethylated cotton.

D.s. 0.04 27.9 46.9 67.5 99.6 D.s. 0.06 41.9 56.7 86.2 99.6 D.S.0.08-. 44.7 69.7 92.2 99.5 D.s 0.10 53.9 75.2 96.5 99.2

Example 4 Samples of untreated cotton cloth and of cloth pretreated as listed in (a) through (g) of Example 1 were 90 oxidized by immersion for 24 hours at room temperature 7 (25 C.) in solution containing 15% by weight of nitrogen dioxide in benzene. The fabrics were washed with methyl alcohol, then with distilled water, and air-dried. Solubilities of the fabrics in 1% aqueous sodium hydroxide 25 and in 1% aqueous sodium carbonate are shown in the following table:

Percent Solubility in- Fabric Oxidized 1% 1% NaOH N21100:;

Untreated cotton 19. 4 13. 9 Carboxymethylated cotton. 99.0 89. 8 Carboxyethylated cotton 99.4 93.5 Phosphonomethylated cotton 95.0 61.0 Alpha-methyl carboxymethylated cotton 90.6 57.0 Methylated cotton 97.0 94. 5 Aminoethylated cotton. 93. 7 74. 1 Mercerized cotton 37. 4 26. 7

Example 5 Samples of 'mercerized cotton cloth and of partially carboxymethylated cotton cloth, degree of substitution 0.10, were oxidized for 24 hours at room temperature (25 C.) by immersion in benzene solutions containing various concentrations of nitrogen dioxide. The resulting fabrics were washed with methyl alcohol, then with distilled water, and air-dried. Solubilities of the fabrics in 1% aqueous NaOH and in 1% aqueous Na CO were determined and are shown in the following table:

oxidizing Percent Solution, Solubility in Fabric Oxidized Percent Nitrogen Dioxide 1% 1% by Weight NaOH Na2C O Mercerized cotton 5 17. 1 11. 3 D0 10 23. 0 15. 2 15 28. 4 l9. 9 20 44. 7 29. 5 1 12. 0 8. 1 3 45. 9 19. 8 5 72. 5 45. 9 1O 96. 7 77. 4 15 98. 9 92. 0 20 99. 9 96. 7

Example 6 7 air-dried. Solubilities of the fabrics in 1% aqueous sodihydroxide solution were determined and are shown in the following table:

Samples of mercerized cotton cloth and of partially carboxymethylated cotton cloth, degree of substitution 0.10, were oxidized by immersion for 17 hours at room temperature (25 C.) in a 25% (by weight) solution of nitrogen dioxide in carbon tetrachloride. The resulting oxidized fabrics were washed with methyl alcohol, then with distilled water and air-dried. Solubil-ities of the samples in 1% aqueous sodium carbonate solution were as follows: Mercerized-oxidized, 92.4%; carboxy-methylatedoxidized, 99.9%.

Example 8 Samples of untreated cotton cloth and of partially carboxymethylated cotton cloth, degree of substitution 0.10, were impregnated with a 40% aqueous solution of sodium nitrite at room temperature and padded to about 100% wet pickup. The samples Were dried at 60 to 70 C. for 7 minutes on pin frames, whereupon they became dry to the touch, and were then treated by immersion at room temperature (approximately 25 C.) in aqueous solutions containing 60, 70, or 80% ortho-phosphoric acid. Upon treatment with the aqueous acid solution, nitrogen dioxide was generated in situ in the fibers for the oxidation step. After 1 hour of reaction, the samples were thoroughly washed with water. Solubilities of the samples in 1% aqueous hydroxide solution were determined and are shown in the following table:

Percent Solubility in We claim:

1. A process comprising subjecting a fibrous cellulosic textile material to chemical modification to substitute therein a radical selected from the group consisting of methyl, ethyl, carboxymethyl, a-methyl carboxymethyl, carboxyethyl, phosphonomethyl, aminoethyl, hydroxyethyl, carbamoylethyl, and sulfoethyl to a degree of substitution of about from 0.02 to 0.12 of said radicals per anhydroglucose unit of the cellulose chain, and oxidizing the resulting chemically modified fibrous cellulosic textile material at a temperature of about from 0 C. to C. for from 15 minutes to 25 hours with nitrogen dioxide to produce a modified fibrous cellulosic textile material characterized in that it is soluble in 1% aqueous alkali, and in that it retains, substantially unaltered, all the useful original textile properties.

2. The process of claim 1 wherein the chemical modifi cation employed is earboxymethylation.

3. The process of claim 1 wherein the chemical modification employed is carboxyethylation.

4. The process of claim 1 wherein the chemical modification employed is phosphonomethylation.

5. The process of claim 1 wherein the chemical modification employed is a-methyl carboxymethylation.

6. The process of claim 1 wherein the chemical modification employed is aminoethylation.

7. The process of claim 1 wherein the chemically modfied fibrous cellulosic material is oxidized for about from 1 to 24 hours at room temperature with a solution of an inert organic solvent containing about from 1 to 25 weight percent of nitrogen dioxide.

8. The process of claim 1 wherein the chemically modified fibrous cellulosic material is oxidized by treatment with nitrogen dioxide generated in situ from aqueous solutions of sodium nitrite and ortho-phosphoric acid.

References Cited in the file of this patent UNITED STATES PATENTS 2,232,900 Yackel Feb. 25, 1941 2,423,707 Kenyon July 8, 1947 2,448,892 Kenyon Sept. 7, 1948 2,472,591 Kenyon June 7, 1949 2,938,765 Reinhardt May 31, 1960 OTHER REFERENCES Reinhardt: Indust. and Engin. Chem., January 1958, pages 83-86.

Drake: Textile Research Journal, March 1959, pages 270-275.

Reinhardt: Textile Research Journal, October 1959,

' pages 802810. 

1. A PROCESS COMPRISING SUBJECTING A FIBROUS CELLULOSIC TEXTILE MATERIAL TO CHEMICAL MODIFICATION TO SUBSTITUTE THEREIN, A RADICAL SELECTED FROM THE GROUP CONSISTING OF METHYL, ETHYL, CARBOXYMETHYL, A-METHYL CARBOXYMETHYL, CARBOXYETHYL, PHOSPHONOMETHYL, AMINOETHYL, HYDROXYETHYL, CARBAMOYLETHYL, AND SULFOETHYL TO A DEGREE OF SUBSTITUTION OF ABOUT FROM 0.02 TO 0.12 OF SAID RADICALS PER ANHYDROGLUCOSE UNIT OF THE CELLULOSE CHAIN, AND OXIDIZING THE RESULTING CHEMICALLY MODIFIED FIBROUS CELLULOSIC TEXTILE MATERIAL AT A TEMPERATURE OF ABOUT FROM 0*C. TO 100*C. FOR FROM 15 MINUTES TO 25 HOURS WITH NITROGEN DIOXIDE TO PRODUCE A MODIFIED FIBROUS CELLULOSIC TEXTILE MATERIAL CHARACTERIZED IN THAT IT IS SOLUBLE IN 1% AQUEOUS ALKALI, AND IN THAT IT RETAINS, SUBSTANTIALLY UNALTERED, ALL THE USEFUL ORIGNAL TEXTILE PROPERTIES. 